1. Field of the Invention
Aspects of the present invention relate to an apparatus to generate a dual transport stream including a normal stream and a turbo stream and a method thereof, and more particularly, to an apparatus to generate a dual transport stream including a normal stream and a turbo stream and a method thereof, which can improve digital broadcasting performance by generating the dual transport stream including the normal stream and the turbo stream robustly processed in order to improve receiving performance of an Advanced Television Systems Committee (ATSC) Vestigial Side Band (VSB) system that is an American-type digital terrestrial broadcasting system.
2. Description of the Related Art
An ATSC VSB system that is an American-type digital terrestrial broadcasting system is a signal carrier type broadcasting system, and uses a field sync signal in the unit of 312 segments. Accordingly, its receiving performance is not good in an inferior channel, and particularly, in a Doppler fading channel.
FIG. 1 is a block diagram illustrating the construction of a transmitter/receiver of an ATSC digital television (DTV) standard as a general American-type digital terrestrial broadcasting system. The digital broadcast transmitter of FIG. 1 is an enhanced VSB (EVSB) system proposed by Philips, which forms and transmits a dual stream provided by adding robust data to normal data of the basic ATSC VSB system.
As illustrated in FIG. 1, the digital broadcast transmitter includes a randomizer 11 to randomize a dual stream, an RS (Reed-Solomon) encoder 12 in the form of a concatenated encoder that adds parity bytes to the transport stream in order to correct errors occurring due to the channel characteristics in a transport process, an interleaver 13 to interleave the RS-encoded data according to a specified pattern, and a ⅔-rate trellis encoder 14 to map the interleaved data onto 8-level symbols by performing a ⅔-rate trellis encoding of the interleaved data. The digital broadcast transmitter performs an error correction coding of the dual stream.
The digital broadcast transmitter further includes a multiplexer 15 to insert a field sync signal and a segment sync signal into the error-correction-coded data as a data format, as illustrated in FIG. 2, and a modulator 16 to insert a pilot tone into the data symbols into which the segment sync signal and the field sync signal have been inserted by adding specified DC values to the data symbols, to perform a VSB modulation of the data symbols by pulse-shaping the data symbols, and to up-convert the modulated data symbols into an RF channel band signal to transmit the RF channel band signal.
In the digital broadcast transmitter, the normal data and the robust data are multiplexed (not illustrated) according to a dual stream system that transmits the normal data and the robust data through one channel, and the multiplexed data is inputted to the randomizer 11. The input data is randomized through the randomizer 11, outer-coded through the RS encoder 12 that is an outer encoder, and then distributed through the interleaver 13. Also, the interleaved data is inner-coded in the unit of 12 symbols through the trellis encoder 14, and then mapped onto the 8-level symbols. After the field sync signal and the segment sync signal are inserted into the coded data, the data is VSB-modulated by inserting a pilot tone into the data, and the VSB modulated data is converted into an RF signal.
On the other hand, the digital broadcast receiver of FIG. 1 includes a tuner (not illustrated) to convert an RF signal received through a channel into a baseband signal, a demodulator 21 to perform a sync detection and demodulation of the converted baseband signal, an equalizer 22 to compensate for a channel distortion of the demodulated signal occurring due to a multi-path, a Viterbi decoder 23 to correct errors of the equalized signal and to decode the error-corrected signal to symbol data, a deinterleaver 24 to rearrange the data distributed by the interleaver 13 of the digital broadcast transmitter, an RS decoder 25 to correct errors, and a derandomizer 26 to derandomize the data corrected through the RS decoder 25 and to output an MPEG-2 transport stream.
Accordingly, the digital broadcast receiver of FIG. 1 down-converts the RF signal into the baseband signal, demodulates and equalizes the converted signal, and then channel-decodes the demodulated signal to restore the original signal.
FIG. 2 illustrates a VSB data frame for use in the American type digital broadcasting (8-VSB) system, into which a segment sync signal and a field sync signal are inserted. As shown in FIG. 2, one frame is composed of two fields, and each field is composed of one field sync segment, which is the first segment, and 312 data segments. Also, one segment in the VSB data frame corresponds to one MPEG-2 packet, and is composed of a segment sync signal of four symbols and 828 data symbols.
In FIG. 2, the segment sync signal and the field sync signal are used for the synchronization and equalization in the digital broadcast receiver. That is, the field sync signal and the segment sync signal refer to known data between the digital broadcast transmitter and receiver, which is used as a reference signal when the equalization is performed on the receiver side.
The American type digital terrestrial broadcasting system as illustrated in FIG. 1 is a system that can form and transmit a dual stream produced by adding the robust data to the normal data of the existing ATSC VSB system. This system transmits the robust data together with the existing normal data.
However, the American type digital terrestrial broadcasting system of FIG. 1 has the problem in that there is almost no effect of improving the inferior receiving performance in a multipath channel due to the transmission of the existing normal data, even though the system transmits the dual stream produced by adding the robust data to the normal data.
That is, there is almost no effect of improving the receiving performance according to the improvement of the normal stream. Also, even with respect to a turbo stream, it does not have a significant effect of improving the receiving performance in a multipath environment. Accordingly, there is a need to generate a dual transport stream having a form in which a turbo stream can be robustly processed.